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We present what we believe to be a new approach of multitone driven amplifier for power scaling and coherent beam combining. A novel multitone seed is generated by a sine wave phase-modulated single-frequency laser and used for stimulated Brillouin scattering suppression of the amplifier. The theory for coherent beam combining of multitone lasers is presented for the first time. We optimize the all-fiber master-oscillator power-amplifier system with high scalability and flexibility based on compact, high efficiency Yb-doped fiber amplifier chain. With this amplifier system, we demonstrated a 275-W high-power output when driven by the phase-modulated single-frequency laser, while the ultimate output power is only 120 W when driven by the single-frequency laser. Scaling this amplifier to a higher power can be expected by adding pumps as the output power is limited by the pumps.